Fixes error and adds text on subsets
Fixes error and adds text on subsets

Also reflows. Refs #114

perl6/doc,MasterDuke17/doc,stmuk/doc,dmaestro/doc,dmaestro/doc,dmaestro/doc,stmuk/doc,tbrowder/doc,perl6/doc,dmaestro/doc,jonathanstowe/doc,stmuk/doc,perl6/doc,dmaestro/doc,jonathanstowe/doc,MasterDuke17/doc,perl6/doc,stmuk/doc,jonathanstowe/doc,MasterDuke17/doc,jonathanstowe/doc,tbrowder/doc,perl6/doc,MasterDuke17/doc,jonathanstowe/doc,stmuk/doc,tbrowder/doc,tbrowder/doc